1. Field of the Invention
The present invention relates generally to mobile telecommunications, and in particular to load balancing in mobile telecommunications networks.
2. Description of the Related Art
CDMA2000, which will be used as an exemplary network, is a 3G mobile telecommunications standard in which the Packet Core Network (PCN) serves as the cornerstone that provides Internet Protocol (IP) services and mobile IP services to mobile nodes (MNs).
A CDMA2000 network comprises, at least logically, a Home Agent (HA), a Foreign Agent (FA), a Packet Data Serving Node (PDSN), a Packet Core Function (PCF) usually co-located with a Base Station Controller (BSC), and an Authentication, Authorisation and Accounting Server (AAA). The HA provides mobile IP services and keeps track of the MNs association with the network, among other things acting like a router when a MN roams in another network, receiving packets intended for the MN and tunnelling them towards the MN, via a FA in the network where the MN is located. The PDSN acts as a kind of gatekeeper, deciding what MNs are allowed to use services and access the network, while the BSC among other things establishes the traffic channel for the MN to use and the PCF decides which PDSN to send the traffic through.
It is advantageous to allow for load sharing between e.g. PDSNs so that for example one particular PDSN is not overloaded while other PDSNs are nearly idle, if possible. A state of the art solution for providing load balancing among PDSNs is shown in FIG. 1. The telecommunications network 110 comprises a co-located BSC/PCF 112 and a PDSN 113. A mobile node (MN) 11 is physically located within the service area of the network 110, but is not yet served by the network 110.
It should be understood that the structure, or architecture, of a PDSN might vary considerably as it is not defined in any standard. In the example, it will be assumed that the PDSN 113 comprises a manager 114 and a plurality of agents of which only one, agent A 115, is shown. The division of a PDSN into manager and agent can be physical, logical or physical and logical. The manager 114 supervises the agents, keeps track of the sessions associated with each agent, collects information about the load of each agent, performs load balancing, if appropriate, and so on. The agents, among other things, handle user data and accounting, provide load information to the manager 114, and contain the Point-to-Point Protocol (PPP) state machines. It is preferred, but not necessary, to colocate the manager and the agents.
The MN 11 sends an origination message 20 to the BSC/PCF 112 to request packet data service. The BSC/PCF 112 may assign a traffic channel 13 to the MN 11 prior to, or in parallel with, the messages described below. The BSC/PCF 112 performs a PDSN selection, step 12, as is well known in the art, by hashing the International Mobile Subscriber Identity (IMSI)—a unique identity—the MN 11, and then using modulo-(number of possible PDSNs) arithmetic on the result to decide which PDSN to use. Thus, unless the number of possible PDSNs changes, the BSC/PCF 112 will always choose the same PDSN for a given IMSI. In this exemplary scenario, the BSC/PCF 112 chooses the PDSN 113 and sends to it a registration request 121, comprising the International Mobile Subscriber Identity (IMSI) of the MN 11.
At the PDSN 113, the manager 114 receives the registration request 121, and selects which agent to use, step 14. The manager 114 keeps a list of active sessions corresponding to the IMSIs, and uses the list to determine if there already is an active session for the IMSI, and if this is the case chooses the agent associated with the session. If there is no active session for the IMSI, then the manager 114 chooses an agent according to some predetermined scheme, such as for example the agent with the least load. As previously mentioned, the manager 114 is aware of the load on each agent that it directly can forward registration requests to.
When the manager 114 has decided which agent should handle the connection, then it returns to the BSC/PCF 112 a registration reply 122 comprising the code ‘136’, indicating that it returns an alternative PDSN IP address, and the alternative address, i.e. the IP address of the selected PDSN, in this case agent A 115. Note that the BSC/PCF 112 has no way of knowing whether the new address is associated with an entity co-located with the manager 114 or not; the BSC/PCF 112 treats it as a second PDSN, even if it is only a agent, as in this case.
Upon reception of the registration reply 122, the BSC/PCF 112 retrieves code ‘136’ and the alternative IP address. The BSC/PCF 112 has a common security association with the manager 114 and the agents that the manager 114 can use, and uses the security association to compute a MN-HA authentication extension that it includes in a second registration request 123 that is sent to agent A 115.
Agent A 115 validates the registration request 123 upon reception, and, if the request 123 is validated, replies with a second registration reply 124. When the second reply 124 has been received, the MN 11 and agent A 115 negotiate a Point-to-Point Protocol (PPP) session 125.
While the above-mentioned method works well, it is however believed that it can be improved. One such improvement is to reduce the signalling between PDSN and BSC/PCF, thereby decreasing the connection set-up time. It can be appreciated that it would be advantageous to have a solution that provides such an improvement. This invention provides such a solution.